Process for spinning polyacrylonitrile



United States Patent 2,696,422 PROCESS FOR SPINNING POLYACRYLONITRILE Erwin Heisenberg, Erlenbach (Main), Germany, assignor to FA. Vereinigte GlanzstotE-Fabriken A. G., Wuppertal-Elberfeld, Germany, a company of Germany No Drawing. Application September 18, 1950, Serial No. 185,497

Claims priority, application Germany November 3, 1949 2 Claims. (Cl. 18-54) Technically useful solvents for the production of spinning solutions for polyacrylonitrile fibres have become known from French patent specifications No. 883,763 and No. 883,764. These are lactams and lactones. In United States Patents Nos. 2,404,713 and 2,404,728, the number of solvents is considerably expanded and the spinning process is described in more detail. The solvents mentioned therein are suitable forpolyacrylonitriles and copolymers consisting of at least 85% acrylonitrile together with other vinyl compounds.

By the use of these solvents spinning solutions are obtained which are colored more or less strongly yellow according to the height of the dissolving temperature. 011 spinning these solutions the yellow coloration is carried over into the spun material. An attempt has been made to shorten the dissolving process as much as possible by observing certain conditions in order to avoid the yellow coloration. See the above mentioned Patents 2,404,713 and 2,404,728. One is forced, however, to work at temperatures at which, as experiments have shown, the yellow coloration in fact appears. Even when less concentrated spinning solutions are used the discoloration cannot be avoided. In the above-mentioned United States patents it is stated that it is advantageous to exclude oxygen while dissolving the polyacrylonitrile. The inventors explicitly point out, however, that this measure is impracticable and in order to avoid the yellow coloration they propose various processes which depend upon speeding up the dissolving process.

Extensive experiments have now shown that, in spite of measures hitherto proposed, the conditions in the spinning head are of particular importance for the yellow coloration of the thread. If the spinning solution supplied to the nozzle is shielded from the action of heat from the spinning chamber, by cooling the spinning solution at the nozzle immediately before emerging into the hot spinning medium, a very substantial improvement in color is surprisingly obtained. There is a further improvement if care is taken to cool down the spinning solution immediately after the dissolving process to a temperature which still just permits of spinning. In both cases, the cooling must of course be adapted to the concentration and molecular weight of the polymer, by cooling less when the molecular weight or concentration is higher than when the molecular weight or concentration is lower.

In order to obtain the most favorable effect it is advantageous to drive out oxygen from the dissolving vessel, filter candle, reservoir and spinning chamber, by an inert gas such as nitrogen. Working under nitrogen and the like does not by itself suffice to remove the yellow coloration from the spinning products. This phenomenon, which at first appears remarkable, is explained by the fact that oxygen dissolved in the spinning solution has an oxidizing and therefore discoloring eifect at higher temperatures. By maintaining low temperatures until the spinning solution enters the spinning chamber in the sense of the present invention, the effect of this dissolved oxygen is practically suppressed.

The method of working is further explained in the following by means of an example:

22.5 kgms. of dimethyl-formamide are introduced into a stirring vessel of 50 litres capacity and 7.5 kgms. of polyacrylonitrile of a molecular weight of 30,000 are added with stirring. The vessel is then evacuated, thereafter filled with oxygen-free nitrogen, and this measure repeated several times so that at most only traces of oxygen can be present in the vessel. Thereupon the temperature is raised with stirring to 100 and maintained for half an hour. The hot solution is forced out of the vessel into a filter candle connected thereto and from the latter into a reservoir. The filter candle and the reservoir connected thereto in gas-tight manner are previously evacuated and filled with nitrogen. The reservoir is set on a spinning head and the spinning solution is forced into the spinning head by means of oxygen-free nitrogen. It is essential to wash out the spinning head carefully with nitrogen before starting spinning.

For spinning solutions of a molecular weight of 30,000 the spinning nozzle is cooled by passing water at 12 C. through a tube which lies closely against the holder of the spinning nozzle and surrounds the nozzle. In the spinning chamber itself nitrogen at 160-170 is blown against the thread.

For spinning solutions of higher molecular weight the temperature of the cooling water must be increased. For 100,000 the temperature is for example C.

The spinning solution in the reservoir above the spinning pump must be kept at temperatures which are adapted to the molecular weight of the polyacrylonitrile. It was found for example that polyacrylonitriles of a molecular weight of approximately 30,000 in a 20% solution in dimethyl-formamide must be kept at room temperature before they are spun in order to suppress the yellow coloration of the spinning material. For polyacrylonitriles of a molecular weight of approximately 100,000 cooling to is necessary. It has been found that in order to avoid discoloration working must always be carried out at the lowest temperature which still permits the viscous solution to be spun.

It is thought that the invention and its advantages will be understood from the foregoing description and it is apparent that various changes may be made in the process without departing from the spirit and scope of the invention or sacrificing its material advantages, the process hereinbefore described being merely a preferred embodiment of the invention.

I claim:

1. A process for the spinning of polyacrylonitrile solutions, comprising the steps of heating polyacrylonitrile in a solvent therefor to a temperature above room temperature sutficient to dissolve the polyacrylonitrile and form a spinning solution, cooling the spinning solution directly after the dissolving process, then cooling the solution again at the spinning nozzle to a temperature which lies so low that the spinning solution can just still be spun through the nozzle, and thereafter spinning the polyacrylonitrile solution through the nozzle into a hot inert gas atmosphere at a temperature substantially higher than the temperature at the spinning nozzle.

2. A process for the spinning of polyacrylonitrile solutions, using a solution of polyacrylonitrile of a molecular weight between about 30,000 and 100,000, compris' ing heating polyacrylonitrile in a solvent therefor to a temperature above room temperature sufficient to dissolve the polyacrylonitrile to form a spinning solution displacing atmospheric oxygen out of the spinning apparatus from the dissolving chamber to the spinning chamber, cooling the spinning solution at the spinning nozzle, to a temperature which lies below the temperature of the hot inert gas atmosphere in the spinning chamber, by the employment, at the nozzle, of a a cooling agent whose temperature lies between about 12 C. and 80 C., the cooling temperature being selected at the lower portion of the aforesaid cooling range for lower molecular weights of the polyacrylonitrile used in the spinning solution, and thereafter spinning the polyacrylonitrile solution through the nozzle into a hot inert gas atmosphere substantlially higher than the temperature at the spinning nozz e.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,233,442 Wiley Mar. 4, 1941 2,318,679 Dreyfus May 11, 1943 2,404,713 Houtz July 23, 1946 2,426,719 Watkins Sept. 2, 1947 

1. A PROCESS FOR THE SPINNING OF POLYACRYLONITRILE SOLUTIONS, COMPRISING THE STEPS OF HEATING POLYACRYLONITRILE IN A SOLVENT THEREFOR TO A TEMPERATURE ABOVE ROOM TEMPERATURE SUFFICIENT TO DISSOLVE THE POLYACRYLONITRILE AND FORM A SPINNING SOLUTION, COOLING THE SPINNING SOLUTION DIRECTLY AFTER THE DISSOLVING PROCESS, THEN COOLING THE SOLUTION AGAIN AT THE SPINNING NOZZLE TO A TEMPERATURE WHICH LIES SO LOW THAT THE SPINNING SOLUTION CAN JUST STILL BE SPUN THROUGH THE NOZZLE, AND THEREAFTER SPINNING THE POLYACRYLONITRILE SOLUTION THROUGH THE NOZZLE INTO A HOT INERT GAS ATMOSPHERE AT A TEMPERATURE SUBSTANTIALLY HIGHER THAN THE TEMPERATURE AT THE SPINNING NOZZLE. 